CL-HTTP is suite of an HTTP 1.1 compliant and SSL-capable tools for creating Web applications written in ANSI Common Lisp that includes: A Sophisticated Server, A Programatic Client, A Caching Proxy, A Reverse Proxy, A Constraint-Guided Web Walker. It comes with a variety of tools for Web development, including high-level, standards-adherent XHTML 1.0 & HTML 4.0.1 generation facilities as well as parsers for HTML & XML, a full text search system, and presentation-based interfaces.

CL-HTTP is an extensive and mature suite of Web tools was developed at the former MIT Artificial Intelligence Laboratory (now merged in 2004 into the MIT Computer Science & Artificial Intgelligence Laboratory). It has been freely available since 1994 and proven in major production applications, including the Electronic Publication System for US White House, 1994-2001. In fact, CL-HTTP was the first HTTP 1.1 compliant server and was used to debug the W3C reference implementation as it inspired the W3C Jigsaw Java implementation.

CL-HTTP provides a highly-abstracted, object-oriented architecture that offers great flexibility and extensibility together with superior efficiency. It is a good choice for advanced Lisp programmers and complex applications. Indeed, CL-HTTP tends to attract more sophisticated and experienced Lisp programmers for reasons that become apparent when it is compared to lesser imitations.

By merely loading a single file, CL-HTTP compiles automatically from source code and starts up right out of the box with an example Web site. There are numerous, if not exhaustive, examples, and the documentation is quite extensive, including configuration instructions and reference manuals, but exploiting the most advanced features may involve reading some of the elegant code.

CL-HTTP runs over major operating systems, and is currently available for a variety of Common Lisp implementations: LispWorks, Symbolics Genera, Allegro CL, MCL, Scieneer Common Lisp, CMUCL, Liquid CL.

CL-HTTP is free in that no payment is required, but most of the source code is copyright by various parties and the license places restrictions on plagerism, piracy, and illegal uses, while requesting that users report both significant applications and code impovements for the benefit of the CL-HTTP community.